1. Field of the Invention:
The present invention relates to an exposure device which enables a suitable exposure to be obtained in a photolithography process for the manufacture of a semiconductor device.
2. Description of the Prior Art:
FIG. 1 schematically shows an example of a known exposure device.
In FIG. 1, the radiation from a light source 11 which may be a mercury lamp irradiates a reticle mask 12 which contains an image of patterns used in a photolithography process. The image on the reticle mask 12 is reduced by a reduction lens system 13, and is then projected onto resist 14 which serves as a photosensitive film, and which has coated the surface of a silicon wafer 15. The silicon wafer is placed on a wafer stage 16. The resist 14 has an exposed portion 17 which represents a portion exposed to the radiation from the light source 11 so as to form a latent image. A photo sensor 18 for measuring the illuminance of the radiation from the light source 11 is disposed between the light source 11 and the reticle mask 12.
The thus-arranged known exposure device is operated in the manner described below. The resist 14 is exposed by a step-and-repeat system or a projection analyzer. During exposure, part of the radiation from the light source 11, such as ultraviolet radiation, is received by the photo sensor 18 which measures the illuminance of the radiation from the light source 11. The brightness of light source 11 deteriorates as time elapses. The time during which a shutter (not shown) is opened is adjusted in accordance with the illuminance measured by photo sensor 18 so that a constant amount of light irradiates the exposed portion 17 from the light source 11.
In other words, exposure is determined by determining through experience the exposed state of the resist 14 which corresponds to the illuminance of the radiation from the light source 11.
In practice, exposure conditions differ in each exposure operation due to variations in the thickness of the resist 14 on the silicon wafer or the state of the resist 14, thereby generating variations in exposure. However, these factors are not taken into consideration when the exposure of the exposed portion 17 is determined.
Thus, the illuminance of radiation from the light source is suitably corrected. However, exposure of the exposed portion is not corrected on the basis of the various factors of the exposed portion, and accurate exposure of the exposed portion is therefore impossible.